[ns] how can you have a string field in a packet header?

[Lori Flynn <lori@cse.ucsc.edu>]

I have a new packet header type, and am having trouble setting a string
value in the header.  Int values get set fine, but the simulation crashes
when I try to set a string.

I use a 'const char *' field for the string (like 'int' for the integer
fields) in the packet header.  I set the string like this:
set thisString "string"
set stringHeaderField $thisString

And in the parsing of "command" (for the 'send' function), the header
field string can be printed.  ie:
printf("The string field in the header is now %s", myHeader->stringValue);
prints out: "The string field in the header is now string"

However, the script crashes in the packet 'recv' function.  The error
message I get, using the GDB debugger, is "no value given for parameter,
Program exited with code 01".